Typically, this type of component may be used within the context of piezoelectric actuators, notably for active optics or actuators for inkjet printers. Such components may also be used for producing resonators and acoustic radio-frequency filters that use a piezoelectric effect for mobile telephony. They are also advantageous for producing ferroelectric variable capacitors, very high value capacitors used for mobile telephony or mobile articles in general (pacemakers, communicating articles).
Currently, to produce planar technology integrated capacitors (referred to as MIM, for Metal Insulator Metal, capacitors), it is necessary to make the electrical contacts on the electrodes. Indeed, a typical structure of an MIM capacitor comprises a layer of dielectric known as functional dielectric DF sandwiched between two electrodes Es and Ei, the bottom electrode being on the surface of a substrate S covered with an insulating layer Ci as illustrated in FIG. 1.
To make the contacts via a contacting layer RCsup and RCinf, and to avoid short-circuiting between the top and bottom electrodes, it is necessary to use an insulating dielectric DI as illustrated in FIG. 2.
This insulating dielectric may be a silicon oxide SiO2 deposited by PECVD, by sputtering, or by spin-coating, commonly identified by the acronym “SOG” for “Spin-on Glass” for example. This may also be a silicon nitride SixNy deposited by PECVD, LPCVD for example, it could just as well be other insulating materials such as the following compounds: Ta2O5, Al2O3, MgO, AlN, etc.
One constraint for this insulating dielectric DI is that it must not disturb the operation of the functional dielectric DF. In particular, it is important that the capacitance that it adds in parallel to the device is negligible relative to the functional capacitance. In order to do this, the prior art uses an insulating dielectric DI of low dielectric constant relative to the functional dielectric DF.
For example, if the functional dielectric DF is Pb(Zr,Ti)O3 (PZT), the dielectric constant of which is typically equal to 1000, it is common to use a silicon oxide as insulating dielectric DI, the dielectric constant of which is equal to 4. Thus, the capacitance added by the SiO2 will be much lower than the capacitance of PZT, at a given equivalent surface area.
For PZT and other oxides having a very high permittivity, the use of the insulating dielectric DI may present a problem of reliability. Indeed, Bouyssou et al. (thesis of Emilien Bouyssou, p. 20, thesis of the University of Tours, 2006) observed that the SiO2 used as insulating dielectric DI is the cause of the appearance of brittleness in PZT capacitors, more precisely of a premature ageing of the capacitors in a constant voltage stress test. This is explained by the hydrogenated compounds used during CVD depositions of insulating dielectrics DI, the most commonly used method in the industry and notably illustrated in FIG. 3, covered with a USG (Undoped Silicon Glass) layer with a contact Rc.